The present invention relates to an apparatus for automatically detecting a called party response in a terminal connected to a telephone line to which a signal representing a called party response is not sent.
In general, when dialing is performed through a public telephone line and a called party responses it, a signal such as a reversing pulse representing a called party response is sent from an exchange, and this signal arrives from a telephone line. In a terminal of a public telephone set and the like, charging is performed in accordance with this signal such as a reversing pulse.
On the contrary, in some foreign countries, the above signal such as a reversing pulse is not sent at all to some telephone lines upon a called party response even if they are connected to public telephone sets. In this case, since charging cannot be performed by a conventional means, a called party response is detected by a special means.
That is, a means for disabling a transmitter of a calling party, and detecting a voice of a called party by an amplifying detector and the like, thereby determining a called party response, a means for detecting a ring back tone in the same manner, and determining a called party in accordance with a predetermined time lapse from completion of detection, or a combination of both means, is generally used.
However, signals sent from a telephone line include a dial tone, a busy tone, and an intercept tone such as talkie guide in addition to a called party voice, and a ring back tone. Therefore, if these signals are detected, they are erroneously determined to be a called party response. As a result, unreasonable charging is performed to cause an unexpected loss to a user.